backup

Backs up the input stream by amount steps. Lexer calls this method if it
had already read some characters, but could not use them to match a
(longer) token. So, they will be used again as the prefix of the next
token and it is the implemetation's responsibility to do this right.

GetImage

Returns a string made up of characters from the marked token beginning
to the current buffer position. Implementations have the choice of returning
anything that they want to. For example, for efficiency, one might decide
to just return null, which is a valid implementation.

GetSuffix

Returns an array of characters that make up the suffix of length 'len' for
the currently matched token. This is used to build up the matched string
for use in actions in the case of MORE. A simple and inefficient
implementation of this is as follows :
{
String t = GetImage();
return t.substring(t.length() - len, t.length()).toCharArray();
}

Done

The lexer calls this function to indicate that it is done with the stream
and hence implementations can free any resources held by this class.
Again, the body of this function can be just empty and it will not
affect the lexer's operation.